Use to replace the default defined by the Email group or <template_from_campaign_id>

mail_from

element

Sender <name> (display name) and <address> (Email address).

Use to replace the default defined by the Email group or <template_from_campaign_id>

reply_to

element

Reply-to Email address.

Use to replace the default defined by the Email group or <template_from_campaign_id>

Use

The reply_to element must be set by the Email group, by <template_from_campaign_id>, or here, even if it is the same as the mail_from address.
If the label is not set, as title will bee used the value of the subject element or its default value if subject is not set

Inheriting header details from an existing campaign template or the Email group

If you do not use any or all of the elements in the <headers> section, XMLDelivery applies the relevant contents from the Email group as the default settings. If, however, you use the <template_from_campaign_id> element, the contents from the campaign template are applied as the defaults instead.

Note:

It is best practice to use a unique <label> (or <subject> if you don’t use the label tag), to be able to readily identify the delivery later.